This invention relates to a natural draft water heater of the type which has a burner at the base of water tank and a central flue which passes up the centre of the water tank for heating water in the tank.
Water heaters of the aforementioned type are well-known and are used extensively for domestic water heating and other applications. The efficiency of such water heaters is considered to be an important consideration by many owners or operators of water heaters.
Generally, the flue leading through the centre of the water tank exits through an exhaust located near the top of the tank. It is important for proper operation of a water heater that the flow of exhaust gases through the tank is not impeded to the extent where the exhaust passage becomes blocked or choked thereby hindering the efficient operation of the tank. For this reason, most tanks have a straight through flow exhaust arrangement.
One problem of the aforementioned type of exhaust arrangement is that the exhaust gases leading through an exhaust outlet from the tank are generally reasonably hot. The heat in the exhaust gases is thus lost to atmosphere with the result that the water heater is not as efficient as it would be if more of the heat were to be extracted from the exhaust gas prior to it exhausting.
A further problem with many water heaters arises as a consequence of the cylindrical shape of a typical water heater. When such a water heater is mounted against a wall, narrow wedge shaped recesses are formed at the back of the water heater which are difficult to clean and can accumulate dirt or provide a haven for rodents or other animals. This could ultimately adversely affect the operation of the heater or provide a potential hazard during operation of the heater.
According to a first aspect of the invention there is provided a water heater comprising:
a generally cylindrical tank which has a central flue which is adapted to be mounted with the cylinder axis generally vertical,
a burner located towards the base of the tank adapted to burn a fuel to discharge heated gases up through the central flue,
a cylindrical flow directing casing surrounding the tank and spaced away from the top and sides of the tank to define a generally annular cylindrical space between the radially outer surface of the tank and the radially inner surface of the casing, said space being in gas flow communication with the upper end of the flue, said annular space having a discharge outlet located at or adjacent the lower most end of the tank,
the arrangement being such that, in use, heated gases pass up the central flue, over the top of the tank, and down the annular space to thereby heat both the radially inner and the radially outer surfaces of the tank prior to exhausting from the heater.
Further there is provided for the casing to be surrounded by a coaxial exhaust cylinder and for the exhaust cylinder to be spaced away from the casing, at least in the lower region of the casing, to thereby define an annular exhaust passage into which the discharge outlet discharges exhaust gases passing from the annular space in use.
Further there is provided an exhaust outlet from said exhaust passage, said exhaust outlet being located at an elevation which is higher than said discharge outlet.
Optionally at least part of the exhaust cylinder is insulated, and preferably at least the major part of the exhaust cylinder is insulated.
The burner is preferably adapted to burn fuel at a sufficiently high temperatures to ensure that the heated gases move up the flue, down the annular space, and up the exhaust passage without clogging, choking or blocking the flow of exhaust gases through the heater.
It is preferred that the exhaust outlet is located at an elevation which is between 20% and 40% of the height of the tank from the base of the tank.
Optionally, the casing may have a flow directing cone shaped protrusion which is positioned on the longitudinal axis of the cylinder and projects downwardly, said protrusion being arranged to guide the flow of gases passing up the flue in a radially outwardly direction, towards the annular space.
According to a second aspect of the invention there is provided a water heater comprising:
a generally cylindrical water tank which is adapted to be mounted with the cylinder axis generally vertical;
a burner located towards the base of the tank adapted to burn fuel to heat water in the tank; and
a generally cylindrical, non-circular housing surrounding the tank said housing having a rear side and a front side, the rear side being of generally planar configuration, the front side being of generally circular, U or parabolic shape in cross section.
The housing may have an air inlet and/or an exhaust outlet in said front side diametrically opposite said rear side. The air inlet and/or exhaust outlet may be located at a height of between 20% and 50% of the height of the housing. The front and rear sides are preferably integrally formed with each other, and the housing may be formed of sheet metal or the like. The housing is preferably specifically adapted to be mounted with the rear side substantially flush against a planar wall to which the water heater is mounted. The water tank is preferably of a configuration having a central flue and having an annular flow passage around the outside of the water tank through which exhaust gases pass prior to exhausting from the housing.
The invention extends to a method of heating water in a cylindrical tank, said method including the steps of passing heated gases up a central flue within the tank, allowing those gases to pass over the top of the tank and down the sides of the tank, and directing those gases to an outlet located at or adjacent the base of the tank. The method preferably includes the further step of directing the gases from the outlet to an exhaust passage which extends upwardly from said outlet to an exhaust outlet located at a higher elevation than the base of the tank.
These and further features of the invention will be made more apparent from the description of preferred embodiments of the invention given below by way of examples. In the description reference is made to the accompanying drawings but specific features shown in the drawings should not be construed as limiting on the invention. Also, where the word xe2x80x9ccomprisingxe2x80x9d or xe2x80x9ccomprisedxe2x80x9d is used in the specification and claims the words, if in doubt, should be interpreted inclusively rather than exclusively.